The technology disclosed herein relates generally to systems and methods for displaying aircraft engine characteristics, such as the operational states of engines, to the flight crew of an aircraft. In particular, the technology disclosed herein relates to display systems and methods for use in indicating the thrust and fan speed of a turbofan aircraft engine.
In controlling the thrust of a turbofan engine, and especially in causing selected changes in the thrust output of such an engine, it is important that a thrust control system provide both accurate and stable indication of thrust. In addition, aircraft are required to provide tachometer indications of engine rotor speeds, including the fan speed (N1). Some commercial transport aircraft with turbofan engines utilize N1 itself as the thrust setting parameter. Providing acceptable accuracy and stability in the display of N1, serving both as a tachometer and as the thrust setting parameter, has been a problem of long standing in the art. This is primarily because the relationship between N1 and thrust is non-linear, resulting in loss of resolution at the upper end (near maximum or takeoff thrust) of the scale. Small changes in N1 at the upper end of the range correspond to large changes in thrust (larger than the same change in N1 at the low end of the fan speed range) This can make pilot determination of a target thrust set difficult due to the low resolution of the display. As a result, a pilot may have difficulty in detecting or setting small thrust increments at high thrust.
It would be advantageous to provide a means for increasing resolution at the upper end of the N1 scale as well as other visual cues for indicating to the pilot that the engine is delivering the desired thrust.